A massive review of the evidence on the safety of the measles, mumps and rubella (MMR) vaccine has concluded that most studies to date have been meaningless, and that more research into the vaccine's long-term effects is needed.

The review found that only 20 out of 3,500 safety studies of MMR could help determine whether it contributes to the development of a variety of conditions, including autism.

Concern about MMR has grown since a controversial report in the Lancet in 1998 linked it to bowel problems and autism. Despite official attempts to reassure parents, immunisation rates have fallen and some parents now choose single vaccines for their children rather than accepting the triple jab offered by the NHS.

The review's author, Dr Thomas Jefferson, criticised the lack of clear design and reporting criteria for vaccine safety studies and called urgently for guidelines.

'In most of the studies we assessed, it was almost impossible to ascertain what had actually been done,' he said. 'The results were certainly deficient. We don't know whether the research was too.'

As co-ordinator of the Cochrane Vaccines Field, part of a respected international collaboration that gathers health care evidence, Jefferson will present the results of the study at a conference in Amsterdam this month. He added: 'We found that vaccination with MMR is unlikely to be associated with bowel problems or autism, and we can say with certainty that without MMR children are vulnerable to a variety of debilitating and potentially fatal illnesses.'

Jefferson, who called for more research into the long-term effects of the vaccine, says the Government has 'refused to listen to people's anxieties and been unwilling to evaluate evidence critically'.